1. Field of the Invention
Embodiments of the invention relate to rotary unions in general, and in particular to a cryogenic rotary union utilizing flexible tubing for use in semiconductor processing applications.
2. Discussion of Related Art
Ion implantation is a process of depositing chemical species into a substrate by bombardment of the substrate with energized ions. In semiconductor manufacturing, ion implanters are used for doping processes that alter the type and level of conductivity of target materials. A precise doping profile in an integrated circuit (IC) substrate and its thin-film structure is important for proper IC performance. To achieve a desired doping profile, one or more ion species may be implanted in different doses and at different energy levels.
FIG. 1 depicts an ion implanter system 1. The ion implanter 100 includes a power source 101, an ion source 102, extraction electrodes 104, a 90° magnet analyzer 106, a first deceleration (D1) stage 108, a 70° magnet analyzer 110, and a second deceleration (D2) stage 112. The D1 and D2 deceleration stages (often referred to as “deceleration lenses”) are each comprised of multiple electrodes with a defined aperture to allow an ion beam to pass therethrough. By applying different combinations of voltage potentials to the multiple electrodes, the D1 and D2 deceleration lenses may manipulate ion energies and cause the ion beam to hit a target workpiece 114 at a desired energy. A number of measurement devices 116 (e.g., a dose control Faraday cup, a traveling Faraday cup, or a setup Faraday cup) may be used to monitor and control the ion beam conditions. Although not shown in FIG. 1, the target workpiece 114 may be supported by a platen which can be used to fix and to move the workpiece during implantation.
It has been discovered that for silicon wafer workpieces, a relatively low temperature during ion implantation is advantageous for amorphization of the silicon wafer. For example, performing ion implantation at temperatures below −60° C. may substantially improve ion implantation process performance. In ion implantation applications, wafers are typically cooled during the implantation process by a cryogenic liquid supplied to a cooling platen, where the cryogenic liquid has been cooled by a chiller.
In addition to cooling, it may be desirable to manipulate the position of the wafer during ion implantation. For example, a rotating platen may be used to clamp the wafer during implant and provide wafer cooling. The rotating platen may allow horizontal and vertical wafer tilt to align the wafer to the ion beam in a desired manner. By allowing the platen to rotate the wafer between passes through the ion beam during implant, the effect of minor beam non-uniformities can be reduced.
One problem with such arrangements is that the cooling fluid, often at cryogenic temperature, must be supplied to the rotating platen. Existing rotary unions, used to couple cryogenic supply tubing to the rotating platen, have proved unsuitable for long term use under such low temperature conditions, and over a large number of cycles. As can be appreciated, leakage of cryogenic fluid is highly undesirable, and thus, there is a need for an improved arrangement for coupling a cryogenic fluid supply to a rotating platen.